feat: AI改写功能集成角色数据 + UI优化

- 新增story_characters表和seed_characters.sql种子数据(27个角色)
- AI改写/续写功能注入角色信息(性别/年龄/外貌/性格)
- 首页UI下移避让微信退出按钮
- 个人中心页面布局重构

client/js/scenes/HomeScene.js

@@ -65,7 +65,7 @@ export default class HomeScene extends BaseScene {
     const stories = this.getFilteredStories();
     const cardHeight = 130;
     const gap = 12;
-    const startY = 175;
+    const startY = 190;
     const tabHeight = 60;
     const contentBottom = startY + stories.length * (cardHeight + gap);
     const visibleBottom = this.screenHeight - tabHeight;
@@ -130,7 +130,7 @@ export default class HomeScene extends BaseScene {
   }
 
   renderContentTabs(ctx) {
-    const tabY = 60;
+    const tabY = 75;
     const tabWidth = (this.screenWidth - 30) / 4;
     const padding = 15;
 
@@ -160,7 +160,7 @@ export default class HomeScene extends BaseScene {
   }
 
   renderCategories(ctx) {
-    const startY = 95;
+    const startY = 110;
     const tagHeight = 28;
     let x = 15 - this.categoryScrollX;
 
@@ -207,7 +207,7 @@ export default class HomeScene extends BaseScene {
   }
 
   renderStoryList(ctx) {
-    const startY = 140;
+    const startY = 155;
     const cardHeight = 130;
     const cardMargin = 12;
     const stories = this.getFilteredStories();
@@ -425,7 +425,7 @@ export default class HomeScene extends BaseScene {
     this.touchStartY = touch.clientY;
     this.hasMoved = false;
 
-    if (touch.clientY >= 90 && touch.clientY <= 130) {
+    if (touch.clientY >= 105 && touch.clientY <= 145) {
       this.isCategoryDragging = true;
       this.isDragging = false;
     } else {
@@ -489,7 +489,7 @@ export default class HomeScene extends BaseScene {
     }
 
     // 分类点击
-    if (y >= 90 && y <= 130) {
+    if (y >= 105 && y <= 145) {
       this.handleCategoryClick(x);
       return;
     }
@@ -530,7 +530,7 @@ export default class HomeScene extends BaseScene {
   }
 
   handleStoryClick(x, y) {
-    const startY = 140;
+    const startY = 155;
     const cardHeight = 130;
     const cardMargin = 12;
     const stories = this.getFilteredStories();